Containers for holding hot electrically conductive materials over an extended period of time at temperatures above liquidus are used in various industrial applications. For example a steel workpiece or article can be dipped into a container holding a hot molten zinc composition to zinc-coat the article in a galvanizing process. The container is generally referred to as a coating pot. The steel workpiece or article dipped into the molten zinc alloy composition may be an individual article, or a continuously moving workpiece, such as a sheet, strip, tube, pipe or a continuous workpiece in other form. Other examples of coating compositions may be zinc alloys or aluminum alloys, such as aluminum-magnesium compositions or zinc-aluminum compositions. The hot molten zinc composition remains in the coating pot for an extended period of time, and must be kept within a nominal temperature range while steel articles are sequentially dipped into the pot, or while a continuous workpiece moves through the pot. While thermal insulation of the pot itself helps in retaining heat, pot insulation alone is generally insufficient to maintain the molten zinc composition at a desired temperature.
Various techniques are used to heat electrically conductive compositions in a coating pot. U.S. Pat. No. 5,354,970 A1 and U.S. Pat. No. 5,787,110 A1 disclose zinc coating pots with one or more coreless electric induction furnaces disposed on the walls of the furnaces. However this results in generally localized heating and molten metal movement in the pots since the coreless electric induction furnaces are stationary and wall mounted relative to the zinc coating material in the pot. Another approach is to use a channel electric induction furnace in the pot as disclosed, for example, in U.S. Pat. No. 1,688,220 A1. Basically a channel induction furnace comprises a solenoidal induction coil wound around magnetic material that is inserted into a tubular volume bounded by refractory material near the bottom region of a coating pot. The channel between the tubular volume's refractory material and the bottom refractory of the coating pot form a flow path for the molten composition (melt) in the pot. Alternating current flow through the solenoidal induction coil creates an electromagnetic field in the channel. The alternating magnetic (flux) field inductively heats the melt in the channel, and applies a magnetic force to the melt that moves the melt through the channel. Therefore a channel furnace provides a combination of induced heating and electromagnetic stirring of the melt. However, one of the disadvantages of a channel furnace is that it complicates the design of the refractory of the pot and adds interfaces between several types of refractory. Each of these interfaces could be the origin of a leak that can result in electrical shorting and malfunction of the coil. In that case, the pot has to be emptied to change the inductor, and the interface between the refractory of the pot and the coil has to be redone. The pot is taken out of service for an extended period of time while the costly refurbishing process is accomplished. Channel inductors are also used in zinc or copper (cathode or anode) melters (or smelters) for heating and stirring a metal composition where zinc or copper is extracted from ore or scrap by an electrolysis (or electrolytic) process, and are subject to limitations in this process similar to those described above for a coating process.
In Japanese patent application publication JP59145772-A (Aug. 21, 1984) a method of removing flux residue from the region in a coating pot containing a molten metal composition where a continuously moving workpiece is dipped into the coating pot is disclosed. The flux is applied to the workpiece prior to dipping in the molten metal and reacts with the molten metal in the pot. However a flux residue accumulates in the region and interferes with the workpiece coating process. An electromagnetic induction apparatus (7) is installed in the pot near the long length of the workpiece (1) to achieve a 1 meter per minute minimum flow velocity of the molten metal to keep the accumulated dross residue out of the region where the workpiece dips into the molten metal so that the flux residue sticking to the workpiece is thoroughly removed, and the cleaned surface of the workpiece reacts with the bath so that a hot dipped workpiece is obtained.
It is one object of the present invention to provide an electric induction heating apparatus and method for heating a hot molten electrically conductive material in a container wherein the heating apparatus can easily be installed and removed from the container so that when the electric induction heating apparatus is submerged in the material in the container the material can be inductively heated.
It is another object of the present invention to provide a combination electric induction heating and stirring apparatus, and method, for heating and stirring a hot molten electrically conductive material in a container wherein the heating apparatus can easily be installed and removed from the container so that when the electric induction heating apparatus is submerged in the material in the container the material can be electromagnetically stirred.
It is another object of the present invention to provide an electric induction heating apparatus, and method, for heating electrically conductive material in a container wherein the heating apparatus can be easily installed and removed from the container so that when the electric induction heating apparatus is submerged in the material in the container when the material is above liquidus temperature the apparatus can be left in the material when the material drops below liquidus or solidus temperature and the apparatus can be used to reheat the material to above solidus or liquidus temperature.